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Old 25th August 2007, 05:24 PM   #1
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Default NAD C521i problems

Hi,

My 5 year old NAD C521i has severe skipping and tracking problems. Both with "pressed" CD's and CD-r's of various brands.
Sometimes it does not read at all, sometimes it starts playing but starts skipping and losing track after a few seconds.

I cleaned the lens and laser-movement-rails with no avail.
I also checked the "RF value" with my 'scope as suggested in some websites, and increased it a bit by carefully adjusting the (only) pot on the laser module to the suggested value of the RF-signal. There are no other pots inside.


Unfortunately, no luck....

Has anybody some suggestions before I throw it in the bin? A new laser module probably? I kinda like the sound of a (working) C521i

Thanks!, Folkert
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Old 25th August 2007, 05:43 PM   #2
anatech is offline anatech  Canada
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Hi Folkert,
Quote:
I also checked the "RF value" with my 'scope as suggested in some websites, and increased it a bit by carefully adjusting the (only) pot on the laser module to the suggested value of the RF-signal.
That was your first mistake. The laser current is marked on the side of the laser head normally. Measure the laser current across the resistor and correct it back to where it was.

Question 1. Sounds like you do not have the manual. Do you?

Question 2. If not, why would you attempt to work on it without the service information?

Quote:
Has anybody some suggestions before I throw it in the bin?
First you need some intelligent information as to what is going on. If you are unwilling to buy the manual, or have it properly serviced then give it to someone who can make use of it. If you won't do that, then bin it. What else can I say?

-Chris
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Old 25th August 2007, 06:33 PM   #3
poynton is offline poynton  United Kingdom
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HI.

You can find the manual here.


http://www.diyaudioprojects.com/Schematics/index.htm



Andy
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Old 25th August 2007, 06:41 PM   #4
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Hi Chris,

Quote:
First you need some intelligent information as to what is going on. If you are unwilling to buy the manual, or have it properly serviced then give it to someone who can make use of it. If you won't do that, then bin it. What else can I say?
Thanks for the reply.
Q1: What makes you think I have no manual? I have the service manual (downloaded from elsewhere on this site).

First thing the manual says is to check is the RF output. I exactly set it to the suggested value, and it looks exactly as described in the servicemanual. And yes, I measured it with my oscilloscope on the testpoint on the main PCB. I tried some 5 different CD's (pressed and CD-r's) and I have a pretty good average value for RF. But in all cases, CD's keep on losing track and start skipping.

In the service manual there's a "faultfinding-tree", but "skipping end losing track" is not in it.

About throwing it away: if it turns out that some fancy servo IC is faulty, then repairing it is not economical because these chips are more expensive than the player itself.
And "binning it" means indeed giving it to somebody who can use it.

Anyway, Since these problems occur more ofted in NAD CD players (see elsewhere on the www.), I more or less was hoping for the "golden tip" or something I completely overlooked.

Thx, Folkert
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Old 25th August 2007, 07:03 PM   #5
anatech is offline anatech  Canada
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Hi Andy,
Didn't have those. Thank you, 'cause now I do!

Hi Folkert,
Quote:
First thing the manual says is to check is the RF output. I exactly set it to the suggested value, and it looks exactly as described in the servicemanual.
Nowhere does the manual say that you should adjust this, it is a check point and you are allowed 5% in level.

Those current presets on the heads are not intended to be adjusted. That is why I didn't think you had the manual. The net is full of information by people who are either not technicians or not properly trained technicians (known from here in as "hackers"). The head had been adjusted at the factory for a known output level. Only Philips has people messing with this setting. The Sony or Sharp heads do not allow this adjustment in the field - rightly so. Hackers will often increase the power and charge you big bucks for not repairing your machine properly.

The one thing you did overlook is ........ the disc motor bearing or feed motor brushes. I will assume that you took the head out (after shorting the pads) and did a full cleaning and lubrication of both the rail and gears to drive the head. At this point you should have checked the disc motor for bad a bearing or shorted brush section.

Remember, a freshly calibrated, good 'scope is only accurate to within a few percent, it's not to be trusted for voltages if it has not been calibrated or is a cheap unit. Your head may have been fine. What you are looking for is the wave form quality with a good pressed CD. Recorded ones have zero value in setting up a CD player.

Quote:
About throwing it away: if it turns out that some fancy servo IC is faulty, then repairing it is not economical because these chips are more expensive than the player itself.
I don't understand this comment at all. If the chip is $30 USD (expensive), you bought this player for less than this? Help me out here please. The question is simply this. Can you repair this player for less than a replacement of equivalent quality will cost you? The equivalent quality part is what trips most people up.

Yes, I've pulled your chain a little here, on purpose. I am challenging your opinions. You have a good player worth keeping. Consider this. If you replaced the entire optical block, you would have what is essentially a brand new player save the tray belts. This would seem to be a worthwhile repair in my book.

-Chris
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Old 25th August 2007, 07:56 PM   #6
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Hi Chris,

I really appreciaty your comprehensive answer, hope the language barrier is not playing tricks on me ;-)

Quote:
Those current presets on the heads are not intended to be adjusted. That is why I didn't think you had the manual. The net is full of information by people who are either not technicians or not properly trained technicians (known from here in as "hackers").
I did not know that. Indeed, you see these "tricks" everywhere on the web. Anyway, I set the pot on the laser head approximately to where it was in the first place; and checked the RF pattern.
It looks normal, although a bit jittering is visible. But I have no reference of a "good" CD player.

Quote:
The one thing you did overlook is ........ the disc motor bearing or feed motor brushes. I will assume that you took the head out (after shorting the pads) and did a full cleaning and lubrication of both the rail and gears to drive the head. At this point you should have checked the disc motor for bad a bearing or shorted brush section.
I did not yet take out the head; I only cleaned the lens (with alcohol and compressed air), and lubed the rails.
I did not check the motors.
To be honest, I don't know how how to check the brushes of the feed motor.
BTW: the problems began when I played a disk, and for instance when I asked the player to go to track 10, it would never reach that track.

Quote:
I don't understand this comment at all. If the chip is $30 USD (expensive), you bought this player for less than this? Help me out here please. The question is simply this. Can you repair this player for less than a replacement of equivalent quality will cost you? The equivalent quality part is what trips most people up.
What I try to explain is that I don't mind spending a few or $$$ on this player, but I need to have a certain chance of success.
And I still thought at that moment, that it still could be a trivial, simple problem to solve (like trimming or cleaning something).
I don't know the value of the player (when it works...), but again, when I can be quite certain what the problem is, I'm willing to spend some bucks.


Quote:
Yes, I've pulled your chain a little here, on purpose. I am challenging your opinions.
No problem it encourages me to really think about this problem!

Regards, Folkert
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Old 25th August 2007, 09:53 PM   #7
anatech is offline anatech  Canada
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Hi Folkert,
Quote:
No problem it encourages me to really think about this problem!
Excellent! That's what I wanted to hear. You will learn from this.

To check the bearings on the disc motor you must remove the CD mechanism. That's the plate with the head and motors on it.

Get it spinning slowly using a variable power supply and a 100 R resistor in series. Rotate the assembly around with the shaft on the horizontal and listen very carefully. If you hear or feel a knocking, the bearing is shot. Motors are cheap. The height of the disc table from the chassis top surface is critical. You need a gauge. You can check for dead windings by placing your scope across the resistor. You can see the wave form of each winding. Look for one that is very different form the others. Check the feed motor the same way, without the gears attached.

I am assuming that you have removed the head and disconnected the sub assy from the main unit.

-Chris
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Old 25th August 2007, 10:37 PM   #8
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Hi Chris,

Thanks again, your information is really food for thought.

BTW: have you information of root causes of this types of problems in CD players? Are disc or laser-motors really prone to problems? More than lasers themselves or driver/servo IC's?

At this moment, the player is assembled and resting on a shelf in the attick.
I'll take it apart again when I have more time, and surely will let the results know in this forum.

Rgds, Folkert (quitting now, it's almost 1:00 am over here)
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Old 26th August 2007, 02:19 AM   #9
anatech is offline anatech  Canada
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Hi Folkert,
Quote:
Are disc or laser-motors really prone to problems? More than lasers themselves or driver/servo IC's?
Yes. They are mechanical and are inexpensively made.

Quote:
BTW: have you information of root causes of this types of problems in CD players?
Just normal wear. Physics rule.

We used to see many laser failures in the early days. The mechanical parts were made to much higher standards. These days the mechanical stuff is almost as cheap as it can possibly be. They expect the electronics to fix these problems. You may see the odd driver IC gone or another IC. There is a failure rate for these. Driver IC's normally point to an electromechanical failure of some kind. A dead winding in a motor will be a common fault. Or a stripped and jammed gear, a jammed track or whatever else can go wrong. Long human hair wrapped around the shaft of a motor is not uncommon. Cat hair, cooking oils and cigarette smoke are all physical problems that can cause electronic components to overheat and fail.

The electronic stuff is really pretty reliable today, not like in the 80's when this stuff just came out.

-Chris
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Old 27th August 2007, 07:26 AM   #10
sangram is online now sangram  India
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FWIW, I had a player that wouldn't read at all, anything - not audio, not CD-Rs, nothing.

It all boiled down to one little belt on the player. It wasn't allowing the tray to fully close and had gone slack, so the pickup was not able to read the disc.

It was one of the smallest belts, I changed it for a few cents and the player worked good as new after that. Of course, YMMV.
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